1. Field of the Invention
The present invention relates to a tandem image forming device including a plurality of image forming means, each of which forms a toner image on a respective image carrier, arranged side by side along an intermediate image transfer body implemented as a belt or along a path for conveying a paper sheet or similar recording medium. Also, the present invention relates to a copier, printer, facsimile apparatus or similar color image forming apparatus including a tandem image forming device.
2. Discussion of the Background
A tandem image forming device includes a plurality of image forming means arranged side by side and each including a charger, an exposing device, a developing device and a cleaning device arranged around an image carrier. Japanese Patent Laid-open Publication No. 9-34205, for example, discloses a color image forming apparatus in which a plurality of image forming means are simply arranged side by side along a path for conveying a paper sheet, OHP (OverHead Projector) film or similar recording medium. Each image forming means electrophotographically forms a toner image in a particular color. Such toner images are sequentially transferred to, e.g., a paper sheet one above the other, completing a composite color image. This kind of apparatus, however, has a problem that the distance between nearby image forming means and therefore the overall size of the apparatus increases.
In light of the above, Japanese Patent Laid-Open Publication No. 9-160471, for example, teaches a tandem image forming device in which one of nearby image forming means has its developing device positioned above a cleaning device included in the other image forming-device. Specifically, a developing device included in each image forming device uses a toner and carrier mixture, i.e., a two-ingredient type developer and is made up of an agitating section and a developing section. The agitating section conveys the developer while agitating the developer to thereby deposit the developer on a sleeve for development. The developing section transfers the toner of the developer from the sleeve to an image carrier. The agitating section is positioned at a higher level than the developing section. The cleaning device of the image forming means next to the above developing means is positioned below the above agitating section.
The tandem image forming device taught in the above Laid-Open Publication No. 9-160471 successfully reduces the distance between nearby image forming means and is therefore small size. Such an image forming device reduces the overall size of the image forming apparatus. However, the developer fed from the agitating section to the developing section, which is lower in level than the agitating section, accumulates on the sleeve. Moreover, after development, the developer accumulated on the sleeve must be returned to the agitating section against gravity and therefore cannot be smoothly circulated or uniformly mixed in the agitating section. Consequently, when the same image pattern is repeatedly output, the consumption of the toner differs from one position to another position, resulting in irregular image density.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 9-269641 and 2000-235311.
It is a first object of the present invention to provide a small size, tandem image forming device capable of preventing a developer from accumulating on a sleeve, promoting smooth circulation of the developer to thereby obviate irregular image density, and reducing a distance between nearby image forming means, and an image forming apparatus including the same and transferring images from the image forming device to a recording medium by way of an intermediate image transfer body.
It is a second object of the present invention to provide an image forming apparatus whose tandem image forming device is reduced in length to thereby further reduce the overall size of the apparatus.
It is a third object of the present invention to further reduce the overall size of an image forming apparatus by locating a cleaning device assigned to an intermediate image transfer body at a unique position.
It is a fourth object of the present invention to ensure, when image formation is interrupted due to an error with toner not contributing to image formation existing on an intermediate image transfer body, high image quality by obstructing the reverse transfer of the toner.
It is a fifth object of the present invention to achieve the fourth object with a simpler configuration.
It is a sixth object of the present invention to provide, in an image forming apparatus of the type transferring images from a tandem image forming device to a recording medium by way of an intermediate image transfer body, the transfer body with a unique configuration on in order to enhance image quality.
It is a seventh object of the present invention to effect desirable secondary image transfer even to a plain paper sheet or similar recording medium having an irregular surface without any irregular density or the expansion or contraction of a toner image.
It is an eighth object of the present invention to prevent, in an image forming apparatus of the type transferring images from a tandem image forming device to a recording medium by way of an intermediate image transfer body, a secondary image transfer device from protruding from the image forming device to thereby reduce the overall size of the apparatus.
It is a ninth object of the present invention to prevent, in an image forming apparatus of the type transferring images from a tandem image forming device to a recording medium by way of an intermediate image transfer body, a fixing device from protruding from the image forming device to thereby reduce the overall size of the apparatus.
It is a tenth object of the present invention to provide, in an image forming apparatus of the type transferring images from a tandem image forming device to a recording medium by way of an intermediate image transfer body, a secondary image transfer device with a unique configuration to thereby reduce the number of parts and cost.
It is an eleventh object of the present invention prevent, in an image forming apparatus of the type transferring images from a tandem image forming device to a recording medium byway of an intermediate image transfer body, an intermediate image transfer body from protruding from the image forming device to thereby reduce the overall size of the apparatus.
It is a twelfth object of the present invention to cancel the slip of a recording medium at the time of pickup with respect to a toner image formed on an image carrier and only roughly matching a write timing for thereby obviating the need for accurate input monitor control customary with a registration sensor.
It is a thirteenth object of the present invention to start writing at a roughly matched timing based on a time when the leading edge of a recording medium moved away from a pickup position is sensed, thereby noticeably reducing the probability of the dislocation of an image too great to be absorbed by a registration roller pair.
It is a fourteenth object of the present invention to noticeably reduce the above probability even in an image forming apparatus of the type providing a preselected distance between consecutive recording media.
It is a fifteenth object of the present invention to roughly control an image formation start timing without resorting to any special sensor and obviate the need for a priority interrupt for sheet sensing, thereby reducing a load on a controller.
It is a sixteenth object of the present invention to prevent, in an image forming apparatus of the type directly transferring images from a tandem image forming device to a recording medium, prevent a developer from accumulating on a sleeve, promote smooth circulation of the developer for thereby obviating irregular image density, and reduce a distance between nearby image forming means for thereby reducing the size of the image forming device and therefore the overall size of the apparatus.
It is a seventeenth object of the present invention to achieve the above objects in a color image forming apparatus.
It is an eighteenth object of the present invention to achieve the above objects in a bicolor image forming apparatus.
It is a nineteenth object of the present invention to facilitate the maintenance of image forming means included in an image forming apparatus.
It is a twentieth object of the present invention to prevent a developer from accumulating on a sleeve included in an image forming apparatus and promote the circulation of a developer to thereby obviate irregular image density.
It is a twenty-first object of the present invention to provide a developing device for an image forming apparatus capable of efficiently agitating a developer with a simple, low-cost configuration to thereby enhance image quality.
It is a twenty-second object at the present invention to provide a developing device for an image forming apparatus capable of freeing an image from critical granularity.
It is a twenty-third object of the present invention to provide a cleaning device for an image forming apparatus capable of exhibiting a desirable cleaning ability to thereby enhance image quality.
It is a twenty-fourth object of the present invention to reduce the size of a charger included in an image forming apparatus.
It is a twenty-fifth object of the present invention to increase a nip width in a fixing device included in an image forming apparatus for thereby enhancing a fixing ability and coping with high-speed image formation.
It is a twenty-sixth object of the present invention to prevent, in an image forming apparatus of the type including a sheet turning device, the sheet turning device from noticeably protruding from a tandem image forming device to thereby reduce the overall size of the apparatus.
It is a twenty-seventh object of the present invention to prevent, in a method of arranging a plurality of image forming means side by side in a tandem image forming device, a developer from accumulating on a sleeve, promote smooth circulation of the developer to thereby obviate irregular image density, and reduce a distance between nearby image forming means for thereby reducing the size of the image forming device and therefore the overall size of the apparatus.
In accordance with the present invention, in a tandem image forming device including a plurality of image forming sections arranged side by side and each including a developing device and a cleaning device arranged around an image carrier, one of nearby ones of the image forming sections has its cleaning device positioned above the developing device of the other image forming section.
Also, in accordance with the present invention, an image forming apparatus includes an intermediate image transfer body implemented as a belt, and a tandem image forming device including a plurality of image foaming sections arranged side by side in a direction in which the intermediate image transfer body extends. The image forming sections each includes a developing device ad a cleaning device arranged around an image carrier. One of nearby ones of the image forming sections has its cleaning device positioned above the developing device of the other image forming section.